A nozzle for making a tubular preform typically has a mandrel, a nozzle body, an annular nozzle insert surrounding the mandrel and forming an annular gap, and positioners for radially acting on the nozzle insert. The mandrel and the nozzle insert are adjustable relative to one another by programmable adjustment motions of the mandrel and/or of the nozzle body during the extrusion of the preforms. This causes the preforms exiting the extrusion nozzle to have a wall thickness profile that changes axially. Angularly, the width of the annular gap can be changed by radially adjusting and/or elastically deforming the nozzle insert. The positioners can be manually actuatable devices or actuators that execute programmable adjustment motions. The programmable adjustment motions of the actuators can be used to change the melt distribution of the preforms angularly of the preform as it exits the extrusion nozzle during preform extrusion. The preforms can be extruded continuously or discontinuously. The preforms exiting the extrusion nozzle are fed to a blow molding cavity of a clamping unit. The preforms are expanded in the blow molding cavity by air after under pressure the interior has been closed to form a hollow plastic member. The preforms can also have a co-extruded multi-layered design.
An extrusion nozzle with the features described above is known from U.S. Pat. No. 7,278,844. The nozzle insert of the known extrusion nozzle has a rigid annular member that has a spherical crown shaped outer surface at the upper end thereof, the surface being pivotably held in a complementary bearing shell. By executing a tilting displacement of the nozzle insert, the width of the annular gap can be changed angularly. However, it is not possible to vary the shape of the annular gap angularly. Furthermore, the spherical bearing of the annular member is expensive to make and subject to wear.
DE 10 2009 058 361 describes an extrusion nozzle that also has the features described above. The nozzle insert of this extrusion nozzle has a rigid end part and an elastically deformable mouth area at the nozzle outlet. The melt passage is sealed off near the separation between the nozzle body and the nozzle insert by an elastically deformable ring seal. The nozzle insert sitting against the ring seal is mounted and tiltable in any direction. The ring seal is subject to high temperatures and pressures in the melt passage of the extrusion nozzle. It must be sufficiently pliable that the nozzle insert supported at the end at the ring seal can make the desired tilting motions. In the event of tilting, the pressure distribution in the ring seal is uneven and areas result where, depending on the tilt angle of the nozzle insert, the ring seal is very compressed and areas where the ring seal is uncompressed, causing the sealing effect to be correspondingly reduced. The sealing of the nozzle ring at a pliable, elastic ring seal is therefore problematic. There is also the danger that during a significant deformation the ring seal projects into the melt passage, producing nonhomogeneities in the melt flow. In the known design, the deformable mouth area is formed in one piece onto the end part. The nozzle insert, which has a rigid end part and a thin-walled, deformable mouth area, is a physically complicated component that is difficult to make and is consequently also an expensive component.
DE 10 2012 022 409 describes an extrusion nozzle that has a three-function component. The three-function assumes three functions important for the use of the extrusion nozzle. It must fulfill a sealing function and facilitate both a tilting motion of the nozzle insert and a longitudinal displacement of the nozzle insert inside the nozzle body. The axial adjustment travel of the longitudinal displacement is dimensioned such that the wall thickness of the tubular preforms exiting the extrusion nozzle can be changed. The three-function component is a temperature-resistant elastomer component that is held in a groove in a positive lock. High demands are placed on the material of the elastomer component. Whether the three-function component can meet these requirements in practice is questionable.